1. Field of the Invention
The present invention relates to the preparation of substrates used in the manufacture of integrated circuits. More particularly, the invention relates to spin-on low dielectric constant (low-k) polymer films on semiconductor substrates. The invention provides a method for achieving non-etchback processing of spin-on low-k polymer films and for retaining the low dielectric constant of spin-on polymer films in areas between metal lines on semiconductor substrates, utilizing electron beam radiation in integration of low-k polymer films into interlevel dielectric (ILD) layers of semiconductor devices.
2. Description of the Prior Art
A continuing trend in semiconductor technology is the formation of integrated circuit (IC) chips having more and faster circuits thereon. Such ultralarge scale integration has resulted in a continued shrinkage of feature sizes with the result that a large number of devices are made available on a single chip. With a limited chip surface area, the interconnect density typically expands above the substrate in a multi-level arrangement and the devices have to be interconnected across these multiple levels. The interconnects must be electrically insulated from each other except where designed to make contact. Usually electrical insulation requires depositing dielectric films onto a surface, for example using a CVD or spinning-on process. The shrinkage in integrated circuit design rules has simultaneously reduced the wiring pitch. These have made the signal propagation delay in the interconnects an appreciable fraction of the total cycle time. The motivation to minimize signal delay has driven extensive studies to develop a low dielectric constant (low-k) material that can be used as interlevel dielectric in integrated circuit (IC) manufacturing. The majority of low-k materials used in the ILD layer are based on thermally cured spin-on organic or inorganic polymers. Although these low-k materials have the desirable low dielectric constant, the integration processes associated with these films are complex, and often require an etchback process followed by capping the dielectric layer using a conventional chemical vapor oxide deposition (CVD). In addition, the dielectric constant of many thermally cured low-k polymer films is not stable and is prone to increase upon exposure to either high temperature encountered in metal deposition, or to oxidative environments such as oxygen plasma used in photoresist stripping. These drawbacks associated with thermally cured spin-on polymer films are often related to their intrinsic features such as low density, susceptibility to moisture absorption, poor thermal stability and susceptibility to oxygen plasma-induced oxidation. Therefore, the integration of many thermally cured spin-on low-k polymers into ILD layers is complex and often requires additional process steps such as etchback and capping. The dielectric constant of many thermally cured low-k polymers is increased during process integration and thus their low-k characteristics are partially or completely degraded upon completing the fabrication of the final semiconductor devices. It is known in the art to use organic polymer dielectrics as the IC interconnect insulator. Such include compositions as polyarylene ethers, fluorinated polyarylene ethers, silsesquioxanes and siloxanes. Examples of other organic polymer dielectrics and articles produced therefrom are disclosed in U.S. Pat. Nos. 5,145,936; 5,108,840; 5,115,082; 5,114,780; 5,155,175; 5,179,188; 5,250,667; 5,235,044; 5,173,542; and 5,270,453. In all these cases, the films are deposited by spin-coating onto a semiconductor substrate and then subjected to a full thermal cure.